Irrigation system for a catheter

ABSTRACT

Described embodiments include apparatus that includes a catheter and a tip electrode, at a distal end of the catheter, shaped to define a plurality of fluid apertures. A structure, within the tip electrode, is configured such that fluid passed distally through a lumen of the catheter flows in a longitudinal direction through a space between the structure and an inner surface of the tip electrode, prior to exiting through the fluid apertures. Other embodiments are also described.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to an application entitled “Ablationcatheter with a flexible printed circuit board,” filed on even dateherewith, and to an application entitled “Ablation catheter with straingauges,” filed on even date herewith.

FIELD OF THE INVENTION

Embodiments of the present invention are related generally to the fieldof medical devices, and specifically to catheters for ablationprocedures.

BACKGROUND

In some ablation procedures, a catheter is inserted into a heart, and anablation electrode at the distal end of the catheter is used to deliveran ablating signal to the tissue.

US Patent Application Publication 2013/0030426, whose disclosure isincorporated herein by reference, describes a catheter adapted forablation having multiple dedicated irrigation tubings to supply fluid totheir respective electrode or set of electrodes. The tubings provideparallel flow pathways through the catheter where irrigation fluid isdelivered to irrigated tip and/or ring electrodes which can accomplishuni-polar or bi-polar ablation. Such separate and dedicated fluidpathways allow fluid to be delivered to the corresponding electrode orset of electrodes at different flow rates. An integrated ablation systemusing such catheter has an ablation energy source and an irrigation pumpwith multiple pump heads that can operate independently of each other.An integrated irrigation tubing set is included to extend between thefluid source and the catheter, with each pump head being able to act ona different tubing that delivers fluid to a different electrode or setof electrodes.

U.S. Pat. No. 8,147,486, whose disclosure is incorporated herein byreference, describes a catheter or lead having a flexible printedcircuit for conveying signals and/or energy. Each trace may be inelectrical connection with one or more external electrical contacts.More specifically, each trace is typically electrically connected to asingle contact. The traces and contacts may assist in diagnosis and/ordetection of bio-electrical signals emitted by organs, and may transmitsuch signals to a connector or diagnostic device affixed to thecatheter. The external electrical contacts may detect bioelectric energyor may deliver electrical or thermal energy to a target site.

PCT Application Publication WO 2014/124231, whose disclosure isincorporated herein by reference, describes a flex-PCB catheter devicethat is configured to be inserted into a body lumen. The flex-PCBcatheter comprises an elongate shaft, an expandable assembly, a flexibleprinted circuit board (flex-PCB) substrate, a plurality of electroniccomponents and a plurality of communication paths. The elongate shaftcomprises a proximal end and a distal end. The expandable assembly isconfigured to transition from a radially compact state to a radiallyexpanded state. The plurality of electronic elements are coupled to theflex-PCB substrate and are configured to receive and/or transmit anelectric signal. The plurality of communication paths are positioned onand/or within the flex-PCB substrate. The communication pathsselectively couple the plurality of electronic elements to a pluralityof electrical contacts configured to electrically connect to anelectronic module configured to process the electrical signal. Theflex-PCB substrate can have multiple layers, including one or moremetallic layers. Acoustic matching elements and conductive traces can beincludes in the flex-PCB substrate.

U.S. Pat. No. 8,529,476, whose disclosure is incorporated herein byreference, describes a medical probe, including a flexible insertiontube, having a distal end for insertion into a body cavity of a patientand which is configured to be brought into contact with tissue in thebody cavity. The probe further includes a sensor tube of an elasticmaterial, contained inside the distal end of the insertion tube andconfigured to deform in response to forces exerted by the tissue on thedistal end. The probe also includes a plurality of strain gauges fixedlyattached to a surface of the sensor tube at different, respectivelocations and configured to generate respective signals in response todeformations of the sensor tube.

SUMMARY OF THE INVENTION

There is provided, in accordance with some embodiments of the presentinvention, apparatus, including:

a catheter;

a tip electrode, at a distal end of the catheter, shaped to define aplurality of microelectrode apertures;

at least one printed circuit board (PCB) disposed within a lumen of thecatheter; and

a plurality of microelectrodes coupled to the PCB and at least partlysituated within the microelectrode apertures, the PCB being configuredto carry signals from the microelectrodes.

In some embodiments, each of the microelectrodes includes:

a conducting element; and

an isolating wall that electrically- and thermally-isolates theconducting element from the tip electrode.

In some embodiments, the apparatus further includes a plurality oftemperature sensors coupled to the PCB, each of the temperature sensorsbeing thermally coupled to the conducting element of a respective one ofthe microelectrodes.

In some embodiments, the microelectrodes are fittingly situated withinthe microelectrode apertures.

In some embodiments, the microelectrodes are fixed to respectiveperimeters of the microelectrode apertures.

In some embodiments, the apparatus further includes a catheter handle ata proximal end of the catheter, wherein the PCB is coupled to thecatheter handle.

In some embodiments, the apparatus further includes a structure disposedwithin a lumen of the tip electrode and configured to inhibit retractionof the microelectrodes through the microelectrode apertures bysupporting the PCB.

In some embodiments, a distal end of the structure is positioned within0.1 mm of a distal face of the tip electrode.

In some embodiments, the structure is annular.

In some embodiments, the tip electrode is further shaped to define aplurality of fluid apertures configured to allow passage of a fluidtherethrough.

In some embodiments, the PCB is positioned within a lumen of the tipelectrode such as to define a space, between the PCB and an innersurface of the tip electrode, for passage of the fluid to the fluidapertures.

In some embodiments, the space is less than 0.3 mm in a radialdirection.

In some embodiments, at least some of the microelectrodes are locatedalong a distal face of the tip electrode.

In some embodiments, the at least some of the microelectrodes that arelocated along the distal face of the tip electrode are orientedobliquely with respect to the distal face of the tip electrode.

In some embodiments, at least some of the microelectrodes are locatedalong a circumferential face of the tip electrode.

There is further provided, in accordance with some embodiments of thepresent invention, a method, including:

using a tip electrode at a distal end of a catheter, passing an ablatingsignal into tissue;

using a plurality of microelectrodes that are coupled to at least oneprinted circuit board (PCB) within a lumen of the catheter, and are atleast partly situated within a plurality of microelectrode apertures inthe tip electrode, acquiring signals from the tissue; and

using the PCB, carrying the signals, and anchoring the tip electrode toa handle of the catheter.

In some embodiments, the method further includes, while passing theablating signal into the tissue, passing a fluid through a plurality offluid apertures in the tip electrode.

In some embodiments, passing the fluid through the fluid aperturesincludes passing the fluid through the fluid apertures via a spacebetween the PCB and the tip electrode.

In some embodiments, passing the fluid through the fluid aperturesincludes passing the fluid through the fluid apertures via a conduitthat is supporting the PCB.

In some embodiments, the method further includes measuring a temperatureof the tissue, using a plurality of temperature sensors that arethermally coupled to respective conducting elements of themicroelectrodes.

There is further provided, in accordance with some embodiments of thepresent invention, apparatus, including:

a catheter;

a tube, at a distal portion of the catheter, including a plurality ofsegments that are at least partly disconnected from each other, and aplurality of bridges that span respective neighboring pairs of thesegments; and

one or more strain gauges, each of the strain gauges being coupled to arespective one of the bridges, and being configured to output a signalin response to bending of the respective one of the bridges.

In some embodiments, each of the strain gauges is coupled to an outersurface of the respective one of the bridges.

In some embodiments, each of the strain gauges is coupled to an innersurface of the respective one of the bridges.

In some embodiments, the tube is shaped to define one or more slots atrespective longitudinal positions along the tube, each of the slotsseparating between a respective pair of the segments.

In some embodiments, each of the slots includes a circumferentialportion that passes circumferentially along the tube, and twolongitudinal portions that pass longitudinally along the tube atrespective ends of the circumferential portion, and a respective one ofthe bridges is between the two longitudinal portions of the slot.

In some embodiments, each of the slots is, circumferentially, between315 and 345 degrees long.

In some embodiments, the apparatus further includes a tip electrode at adistal end of the catheter, the tube being electrically coupled to thetip electrode.

In some embodiments, the tip electrode and the tube are formed of asingle piece of material.

In some embodiments, the tube is metallic.

In some embodiments, the apparatus further includes at least one printedcircuit board (PCB) disposed within the tube and configured to carry thesignals from the strain gauges.

In some embodiments, the strain gauges are mounted on the PCB.

In some embodiments, the apparatus further includes a structure thatsupports the PCB, the structure being coupled to the tube.

In some embodiments, the structure includes a plurality of tabs, and thestructure is coupled to the tube by virtue of the tabs fitting intocomplementary apertures in the tube.

In some embodiments, the structure includes a conduit configured toallow passage of a fluid therethrough.

In some embodiments, the strain gauges include three strain gaugesdisposed at different respective circumferential positions along thetube.

There is further provided, in accordance with some embodiments of thepresent invention, a method, including:

using a tip electrode at a distal end of a catheter, passing an ablatingsignal into tissue,

-   -   the catheter including a tube that includes a plurality of        segments that are at least partly disconnected from each other,        and a plurality of bridges that span respective neighboring        pairs of the segments; and

while passing the ablating signal into the tissue, estimating a forceapplied to the tissue by the catheter, using a plurality of straingauges coupled to the bridges.

In some embodiments, the method further includes, while passing theablating signal into the tissue, passing a fluid through a plurality offluid apertures in the tip electrode.

In some embodiments, the passing the fluid through the plurality offluid apertures includes passing the fluid through the plurality offluid apertures via the tube.

In some embodiments, estimating the force includes:

using the strain gauges, outputting signals in response to bending ofthe bridges, and

based on the signals, estimating the force.

In some embodiments, the method further includes, using a printedcircuit board (PCB) disposed within a lumen of the catheter, carryingthe signals to a proximal end of the catheter.

There is further provided, in accordance with some embodiments of thepresent invention, apparatus, including:

a catheter;

a tip electrode, at a distal end of the catheter, shaped to define aplurality of fluid apertures; and

a structure, within the tip electrode, configured such that fluid passeddistally through a lumen of the catheter flows in a longitudinaldirection through a space between the structure and an inner surface ofthe tip electrode, prior to exiting through the fluid apertures.

In some embodiments, the structure is configured such that fluid flowsthrough the space in a distal direction.

In some embodiments, the structure is configured such that the fluidflows through the space in a proximal direction.

In some embodiments, the structure includes a conduit.

In some embodiments, the conduit is configured such that the fluid exitsa distal opening of the conduit, and is then deflected into the space bya distal face of the tip electrode.

In some embodiments, a majority of the fluid apertures are in acircumferential face of the tip electrode.

In some embodiments, the distal opening of the conduit is positionedwithin 0.3 mm of the distal face of the tip electrode.

In some embodiments, the structure is shaped to define one or morecircumferential openings, such that the fluid flows into the spacethrough the circumferential openings.

In some embodiments, the space is less than 0.3 mm in a radialdirection.

In some embodiments, at least part of the space is less than 0.1 mm in aradial direction.

There is further provided, in accordance with some embodiments of thepresent invention, a method, including:

using a tip electrode at a distal end of a catheter, passing an ablatingsignal into tissue; and

while passing the ablating signal into the tissue, causing fluid to flowin a longitudinal direction through a space between a structure and aninner surface of the tip electrode, and to subsequently exit the tipelectrode through fluid apertures in the tip electrode.

In some embodiments, causing the fluid to flow in the longitudinaldirection includes causing the fluid to flow in a distal direction.

In some embodiments, causing the fluid to flow in the longitudinaldirection includes causing the fluid to flow in a proximal direction.

In some embodiments, the structure includes a conduit, and the methodfurther includes causing the fluid to flow through the conduit prior toflowing through the space.

In some embodiments, the method further includes causing the fluid toexit a distal opening of the conduit, and to be deflected into the spaceby a distal face of the tip electrode.

In some embodiments, the distal opening of the conduit is positionedwithin 0.3 mm of the distal face of the tip electrode.

In some embodiments, the method further includes causing the fluid toflow into the space through one or more circumferential openings in thestructure.

In some embodiments, a majority of the fluid apertures are in acircumferential face of the tip electrode.

In some embodiments, the space is less than 0.3 mm in a radialdirection.

In some embodiments, at least part of the space is less than 0.1 mm in aradial direction.

The present invention will be more fully understood from the followingdetailed description of embodiments thereof, taken together with thedrawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a procedure using an ablationcatheter, in accordance with some embodiments of the present invention;

FIG. 2 is a schematic illustration of the distal end of a catheter, inaccordance with some embodiments of the present invention;

FIG. 3 is a schematic illustration of a slotted tube, in accordance withsome embodiments of the present invention;

FIG. 4 is a schematic illustration of a longitudinal cross-section ofthe distal end of a catheter, in accordance with some embodiments of thepresent invention; and

FIG. 5 is a schematic illustration of an ablation catheter, inaccordance with some embodiments of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS Overview

Embodiments described herein include an ablation catheter for use inablating tissue, such as intracardiac tissue. The catheter comprises atip electrode at the distal end of the catheter, which is used todeliver ablating signals to the tissue. The catheter further comprises aplurality of microelectrodes, which are coupled to at least one printedcircuit board (PCB) disposed within the lumen of the catheter. Themicroelectrodes are fittingly situated within microelectrode aperturesin the tip electrode. During the ablation procedure, the microelectrodesmay be used to acquire signals from the tissue, in order to help assessthe electrical activity of the tissue. These signals may be carried bythe PCB to the proximal end of the catheter.

Advantageously, the microelectrodes, and the PCB to which they arecoupled, serve a structural role, in addition to the functional roledescribed above. In particular, the fit of the microelectrodes withinthe microelectrode apertures, and the attachment of the microelectrodesto the PCB, inhibits the tip electrode from migrating from the rest ofthe catheter, such that it may not be necessary to have a separate“safety wire” holding the tip electrode. Typically, a conduit, or othersupport, within the tip electrode supports the PCB, such that themicroelectrodes do not migrate from the microelectrode apertures.

During the ablation procedure, it is typically desired to pass anirrigating fluid into the blood surrounding the catheter, in order (i)to draw heat from the ablating tip, and (ii) to help prevent blood clotsfrom forming. Hence, the tip electrode is typically shaped to define aplurality of fluid apertures, for passage of an irrigating fluidtherethrough. Advantageously, embodiments described herein allow for alarge amount of heat exchange between the tip electrode and theirrigating fluid, by providing, for passage of the fluid, a narrow spacebetween the PCB and the tip electrode, along the inner surface of thetip electrode. As the fluid is forced through this narrow space prior toexiting from the fluid apertures, a large amount of heat is absorbedfrom the tip electrode. In some embodiments, to pass the fluid throughthe narrow space, the fluid is deflected by the distal inner face of thetip electrode.

To increase the efficacy and/or safety of the ablation procedure, it istypically helpful to regulate the force applied to the tissue by thecatheter. To this end, the catheter described herein typically furthercomprises a slotted tube, which is disposed within the lumen of thecatheter, near the distal end of the catheter. A plurality of slotsalong the tube divide the tube into separate segments, each neighboringpair of the segments being spanned by a respective bridge. A pluralityof strain gauges are coupled, respectively, to the bridges. As thecatheter pushes against the tissue at the contact point between the tipelectrode and the tissue, the force applied to the catheter by thetissue causes the bridges to bend. The strain gauges measure thisbending, and output signals in response thereto. Based on these signals,the magnitude and direction of the force may be estimated, such that theforce may be appropriately regulated.

Apparatus Description

Reference is initially made to FIG. 1, which is a schematic illustrationof a procedure using an ablation catheter 22, in accordance with someembodiments of the present invention. FIG.

depicts a physician 34 using catheter 22 to perform an ablation oftissue within a heart 25 of a subject 26. Catheter 22 comprises acatheter shaft 82, at a distal end of which is disposed a tip electrode24. During the ablation procedure, tip electrode 24 is inserted intoheart 25. Tip electrode 24 is then brought into contact with theintracardiac tissue, and ablating signals are passed, via the tipelectrode, into the tissue.

A console 36, which is connected to the ablation catheter via a catheterhandle 84 at the proximal end of the catheter, includes a signalgenerator (“SIG GEN”) 28, which generates the ablating signals, aprocessor (“PROC”) 30, which receives and processes signals receivedfrom the distal end of the catheter, and a pump 31, which pumpsirrigating fluid to the distal end of the catheter. During theprocedure, anatomical information, and/or any other relevantinformation, may be displayed on a monitor 38.

Tip electrode 24 is shaped to define a plurality of microelectrodeapertures 32, within which, respectively, a plurality of microelectrodes40 are fittingly situated. (Typically, the microelectrodes areelectrically and thermally isolated from the tip electrode.) In general,any number of microelectrode apertures 32—and hence, microelectrodes40—may be located along the distal face 42 of the tip electrode, and/orthe circumferential face 44 of the tip electrode. In some embodiments,for example, catheter 22 comprises six microelectrodes—three at distalface 42, and three at circumferential face 44, the latter threemicroelectrodes being spaced apart from each other by approximately 120degrees. Each of the microelectrodes may either be flush with the outersurface of the tip electrode, or alternatively, may protrude from theouter surface. (Such protrusion may facilitate a more accuratetemperature reading by a temperature sensor located beneath themicroelectrode, as described below, by bringing the temperature sensorcloser to the tissue from which the reading is acquired.) Upon the tipelectrode being placed in contact with the tissue, the tip electrodepasses an ablating signal into tissue, while the microelectrodes acquireintracardiac electrocardiogram (ECG) signals from the tissue.Alternatively or additionally, the microelectrodes may be used to passcurrent into the tissue for impedance measurements, which may be used,for example, for impedance-based location-sensing.

Typically, tip electrode 24 is further shaped to define a plurality offluid apertures 50, which are configured to allow passage of a fluidtherethrough. During the ablation procedure, while ablating signals arebeing passed into the tissue, an irrigating fluid is delivered to, andpassed through, fluid apertures 50, as further described below. Thefluid apertures are typically much smaller than the microelectrodeapertures, and are typically located mostly (or entirely) along thecircumferential face of the tip electrode, i.e., typically most, or all,of the fluid apertures pass through the circumferential face.

Typically, catheter 22 further comprises a slotted tube 46, which istypically situated at a distal portion of the catheter, such asimmediately proximally to, and/or partly underneath, tip electrode 24.(For example, the proximal end of the tip electrode may slide over thedistal portion of the tube.) As described in detail below, tube 46 isshaped to define one or more slots 70 at respective longitudinalpositions along the tube, each of slots 70 separating between tworespective segments of the tube, such that the segments are at leastpartly disconnected from each other. Each pair of neighboring segmentsis spanned by a bridge 74. One or more strain gauges 48 are coupled tobridges 74, each strain gauge 48 being configured to measure the strainin the bridge to which the strain gauge is coupled. As described above,these measurements may be used to estimate the force applied to thetissue by the catheter during the ablation procedure. Typically, slottedtube 46 is metallic; for example, the slotted tube may be manufacturedfrom any suitable metallic alloy, such as nitinol.

Although, in FIG. 1, the slotted tube and strain gauge are seen througha transparent portion of the outer surface of the catheter, it is notedthat the portion of the outer surface of the catheter that covers theslotted tube is not necessarily transparent. It is further noted that,in some embodiments, the slotted tube is not covered, such that theslotted tube itself constitutes part of the outer wall of the catheter,as shown in FIG. 5, which is described below.

In some embodiments, catheter 22 further comprises one or more ringelectrodes 21 on the surface of the catheter. Ring electrodes 21 may beused, for example, for ECG-signal acquisition, or injection of currentfor impedance-based location-sensing.

Reference is now made to FIG. 2, which is a schematic illustration ofthe distal end of catheter 22, in accordance with some embodiments ofthe present invention. (In FIG. 2, tip electrode 24 is hidden, such thatthe components of the catheter underneath the tip electrode arevisible.)

Typically, at least one flexible PCB 58 is disposed within the lumen ofthe catheter. For example, FIG. 2 shows a single PCB 58, comprisingthree splines that are folded over such that the splines extendproximally from the distal end 62 of PCB 58. PCB 58 typically runsthrough the lumen of the catheter, such that the PCB is covered bycatheter shaft 82, i.e., the PCB is typically not exposed. In someembodiments, PCB 58 extends from the distal end of the catheter tocatheter handle 84, and is directly coupled to the catheter handle. Inother embodiments, the proximal end of PCB 58 is connected to a cable,and the cable is coupled to the catheter handle. In either case, thecoupling of the PCB to the catheter handle—whether a direct coupling, ora coupling via a cable—anchors the PCB (and hence, the tip electrode, asfurther described below) to the catheter handle.

As shown in FIG. 2, microelectrodes 40 are coupled to the PCB, and thePCB carries signals from the microelectrodes to the proximal end of thecatheter. In some embodiments, PCB 58 also carries signals to the distalend of the catheter. For example, PCB 58 may carry current, forinjection into tissue, to ring electrodes 21 (FIG. 1). Alternatively oradditionally, PCB 58 may carry signals, such as current signals forinjection for impedance measurements, to the microelectrodes, and/orablating signals to the tip electrode via an electrical coupling betweentube 46 and tip electrode.

Typically, each microelectrode comprises a conducting element 66 and anisolating wall 64. Isolating wall 64, which is typically glued to PCB58, surrounds conducting element 66, thus electrically- andthermally-isolating the conducting element from the tip electrode.Conducting element 66 is typically electrically coupled to PCB 58 (e.g.,by being directly connected to the PCB), such that ECG signals detectedby the conducting surface may be carried by the PCB from the distal endof the catheter. In some embodiments, as shown, each microelectrode iscylindrically shaped, whereby isolating wall has an annular shape, andthe outer surface of conducting element 66, which forms the top of thecylinder, is circular. Typically, the diameter of the microelectrodeapertures in the tip electrode is only slightly larger than that of themicroelectrodes, such that the microelectrodes fit snugly into theapertures. Alternatively or additionally, during the manufacture ofcatheter 22, the microelectrodes may be glued to, or otherwise fixed to,the respective perimeters of the microelectrode apertures. Thus, themicroelectrodes are securely coupled to the tip electrode.

Typically, temperature sensors 60, such as thermistors, are also coupledto the PCB, and the PCB further carries signals from temperature sensors60. Typically, each temperature sensor is located within a respectiveisolating wall 64, beneath the outer surface of a respective conductingelement 66. (For clarity, in FIG. 2, the conducting element of one ofthe microelectrodes is hidden, revealing a temperature sensor 60.) Insuch embodiments, conducting elements 66 are thermally coupled to thetemperature sensors (e.g., by contacting the temperature sensors), suchthat the conducting elements conduct heat from the tissue to thetemperature sensors, thus facilitating the measuring of the tissuetemperature by the temperature sensors.

Although the tip electrode is typically fastened to the remainder of thecatheter (e.g., by being fastened to tube 46), a fallback securementmechanism for the tip electrode may be desired. Advantageously, as notedabove, the PCB, together with the microelectrodes, serve as such afallback securement mechanism, by anchoring the tip electrode to theremainder of the apparatus. For example, the tip electrode may beanchored to the catheter handle, by virtue of the PCB—which is attachedto the microelectrodes, which are securely coupled to the tipelectrode—being connected to the catheter handle. It may thus beunnecessary to attach a safety wire, or any other dedicated fallbacksecurement mechanism, to the tip electrode. The PCB thus providesstructural stability to the catheter, in addition to carrying signals toand/or from the distal end of the catheter.

In some embodiments, one or more of the microelectrodes at distal face42 are oriented obliquely (e.g., at 45 degrees) with respect to distalface 42. Such an orientation further helps to anchor the tip electrodein place, by inhibiting the tip electrode from sliding distally.

Typically, PCB 58 is supported by a conduit 54, which, aside fromsupporting PCB 58 (and hence inhibiting the microelectrodes fromretracting, i.e., sliding inward from the surface of the tip electrodeinto the lumen of the tip electrode), also allows passage of fluidtherethrough. Conduit 54 is shaped to define a distal opening 57, i.e.,an opening at the distal end of the conduit, through which, as furtherdescribed below, irrigating fluid may pass. As shown in FIG. 2, conduit54 may be coupled to slotted tube 46, e.g., via tabs 47 of the conduitthat fit into complementary apertures 49 in the slotted tube.

Alternatively or additionally to conduit 54, PCB 58 may be supported byany other structure, such as an annular supporting structure, thatprevents radially-inward migration of the microelectrodes.

Reference is now made to FIG. 3, which is a schematic illustration ofslotted tube 46, in accordance with some embodiments of the presentinvention. As described above, slotted tube 46 is shaped to define oneor more slots 70, at respective longitudinal positions along the tube,which divide the tube into a plurality of segments. For example, in FIG.3, three slots divide the tube into four segments—a first segment 72 a,a second segment 72 b, a third segment 72 c, and a fourth segment 72 d.Typically, the slotted tube is formed by laser-cutting the slots into anuncut tube.

Each of slots 70 typically includes, in addition to a circumferentialportion 78 that passes circumferentially along the tube, twolongitudinal portions 80 that pass longitudinally along the tube atrespective ends of circumferential portion 78. (Longitudinal portions 80thus “cut into” the segments.)

Between the two ends of each longitudinal portion 80 lies a respectivebridge 74, which spans the pair of neighboring segments separated by theslot. In response to forces applied to the catheter, bridges 74 bend.Typically, each of the slots runs along a large majority of thecircumference of the tube, such that each bridge 74 is relativelynarrow. For example, each slot may be, circumferentially, between 315and 345 degrees long (i.e., each slot may pass along 315-345 degrees ofthe circumference of the tube), such that bridge 74 is between 15 and 45degrees wide. The relative narrowness of the bridges facilitates thebending of the bridges.

As shown in FIG. 3, strain gauges 48 are typically coupled to bridges74, such that each strain gauge spans a respective pair of segments. (InFIG. 3, the rightmost strain gauge is not shown, due to this straingauge being located at a portion of the tube that faces away from theviewer.) The bending of each bridge 74 causes a signal to be output bythe strain gauge that is coupled to the bridge, the signal indicatingthe strain in the bridge. The signals from the strain gauges arecarried, by PCB 58, to the proximal end of the catheter.

For example, each strain gauge shown in FIG. 3 comprises a resistor 76.As the shape of the strain gauge changes due to the strain in thebridge, the resistance of resistor 76 changes. Via PCB 58, a voltage maybe applied across the strain gauge, such that the measured currentflowing through the strain gauge indicates the change in resistance ofthe strain gauge, and hence, the strain in the bridge. Alternatively, acurrent may be applied across the strain gauge, such that the measuredvoltage across the strain gauge indicates the change in resistance ofthe strain gauge. This measured voltage or current is referred to hereinas the “signal,” output by the strain gauge, that indicates the strainin the bridge.

Based on the signals from strain gauges 48 that indicate the strainmeasurements, the force that is being applied to the catheter may beestimated. In particular, by placing three strain gauges at differentrespective circumferential positions along the tube, three separate,independent strain measurements may be obtained. Based on these threestrain measurements, the direction of the force, in addition to themagnitude of the force, may be ascertained. For example, as shown, thethree strain gauges may be spaced equiangularly along the tube, suchthat 120 degrees separates between the respective middles of any two ofthe strain gauges.

In some embodiments, as shown, strain gauges 48 are coupled to the outersurfaces of the bridges. In such embodiments, connecting elements (notshown) may connect the strain gauges to the PCB disposed within thetube, such that the PCB may carry the signals from the strain gauges. Inother embodiments, strain gauges 48 are coupled to the inner surfaces ofthe bridges. In such embodiments, the strain gauges may be mounted onthe PCB.

Reference is now made to FIG. 4, which is a schematic illustration of alongitudinal cross-section of the distal end of catheter 22, inaccordance with some embodiments of the present invention.

As described above, during the ablation procedure, pump 31 deliversirrigating fluid to the distal end of the catheter. FIG. 4 shows anexample flow pattern of this irrigating fluid, as the irrigating fluidapproaches, and then passes through, tip electrode 24. First, the fluidpasses through tube 46, and then through conduit 54. Next, the fluidpasses through opening 57 of the conduit and through an opening 56 atthe distal end of the PCB. The fluid thus reaches distal face 42 of thetip electrode, and is subsequently deflected, by the inner surface 68 ofdistal face 42, into a space 71 that lies between (i) the PCB andconduit, and (ii) the tip electrode. (Space 71 is typically situatedprimarily adjacent to circumferential face 44 of the tip electrode.)After flowing, through space 71, along the inner surface of the tipelectrode, the fluid reach fluid apertures 50, and exits from the tipelectrode via the fluid apertures.

Typically, the fluid, as it flows distally through the lumen of thecatheter, is contained by the catheter, such that all, or at least asubstantial majority of, the fluid reaches opening 57 of the conduit,and then flows proximally through space 71, as described above. In thisregard, it is noted that any slots 86 adjacent to tab 47 are typicallyrelatively narrow, such that relatively little fluid escapes from slots86. It is further noted that any fluid that escapes through slots 70,between segments of tube 46, typically does not reach space 71; rather,the path of this fluid is blocked by tip electrode 24.

Notwithstanding the above, in some embodiments, catheter 22 comprises afluid-delivery tube, which delivers fluid to the distal end of thecatheter. For example, the distal end of such a fluid-delivery tube maybe connected to the proximal end of conduit 54, such that fluid flowsthrough the fluid-delivery tube to conduit 54, and then through conduit54 as described above. Alternatively, for example, the distal end ofsuch a fluid-delivery tube may be immediately proximal to (e.g., within0.1 mm of) inner surface 68, such that the fluid reaches inner surface68 immediately upon exiting the fluid-delivery tube.

In some embodiments, catheter 22 does not comprise conduit 54. In suchembodiments, the portion of the PCB that is distal to tube 46 may beclosed (i.e., the openings between the PCB splines may be closed), suchthat the PCB functions as a conduit, in that the fluid flows through thePCB to the distal face of the tip electrode.

Typically, the PCB and conduit are positioned within the tip electrodesuch that space 71 is relatively narrow. For example, the portion of thespace that is between the PCB and the tip electrode may be less than 0.1mm in the radial direction, i.e., the width W1 of the space, measuredbetween the PCB and the inner surface of the tip electrode, may be lessthan 0.1 mm. (Assuming the thickness of the PCB is approximately 0.2 mm,this implies that the portion of the space between conduit 54 and theinner surface of the tip electrode may be less than 0.3 mm.) Thenarrowness of space 71 forces the fluid to flow near the inner surfaceof tip electrode 24, along a large portion of this surface, such that arelatively large amount of heat is transferred from the tip electrode tothe fluid.

Typically, the majority of the fluid apertures are in thecircumferential face of the tip electrode, rather than the distal face,such that relatively little fluid escapes from the catheter, prior toflowing through space 71. Thus, a relatively large amount of heat may betransferred from the tip electrode to the fluid. For example, in someembodiments, distal face 42 does not have any fluid apertures, such thatall of the fluid is forced into space 71. Alternatively, some fluidapertures may be positioned within distal face 42.

Typically, distal opening 57 is positioned relatively close to distalface 42, e.g., within 0.3 mm of the distal face. Typically, the distalend of the conduit is flush with the distal end of the PCB, with distalopening 57 being aligned with distal opening 56 of the PCB. Thus, all ofthe fluid exiting through distal opening 57 is forced through distalopening 56, emerging from distal opening 56 within a small distance D1,which may be less than 0.1 mm, of distal face 42.

Were the conduit positioned more proximally, some of the fluid exitingfrom opening 56 might flow directly to the fluid apertures, withoutfirst flowing along the inner surface of the tip electrode. Bypositioning the conduit near the distal face, therefore, the fluid isforced to flow along the inner surface of the tip electrode, prior toexiting from the tip electrode.

As described above, FIG. 4 shows a flow pattern according to which thefluid flows, along the inner surface of the tip electrode, mainly in aproximal direction. Alternatively or additionally, the fluid may flow inthe opposite longitudinal direction, i.e., the distal direction, alongthe inner surface of the tip electrode. For example, tabs 47, and/orother portions of conduit 54 (or of any other structure positionedwithin the tip electrode), may be shaped to define one or morecircumferential (or “side”) openings 88, such that the irrigating fluidflows through openings 88 into space 71, flows distally through space71, and exits through the fluid apertures. (In such embodiments, thedistal end of the conduit is typically closed, such that fluid does notflow directly to the distal face of the tip electrode.) In suchembodiments, the majority, or all, of the fluid apertures may be locatedon the distal face of the tip electrode, such that most, or all, of thefluid forced into space 71 flows along most of the length of the tipelectrode, prior to exiting from the tip electrode.

Reference is now made to FIG. 5, which is a schematic illustration of anablation catheter, in accordance with some embodiments of the presentinvention. In the embodiment shown in FIG. 5, tip electrode 24 and tube46 are formed from a single piece of material, e.g., a single piece ofnitinol, such that the tip electrode is continuous with the tube.(Stated differently, in the embodiment of FIG. 5, the distalmost segmentof tube 46 functions as the tip electrode.) This embodiment thus differsfrom previously-described embodiments, in which the tip electrode andthe tube are manufactured separately, and are then physically and/orelectrically coupled to one another. Advantages of such a design includesimplicity of, and reduced cost of, manufacture.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed hereinabove. Rather, the scope of embodiments of the presentinvention includes both combinations and subcombinations of the variousfeatures described hereinabove, as well as variations and modificationsthereof that are not in the prior art, which would occur to personsskilled in the art upon reading the foregoing description. Documentsincorporated by reference in the present patent application are to beconsidered an integral part of the application except that to the extentany terms are defined in these incorporated documents in a manner thatconflicts with the definitions made explicitly or implicitly in thepresent specification, only the definitions in the present specificationshould be considered.

1. Apparatus, comprising: a catheter; a tip electrode, at a distal endof the catheter, shaped to define a plurality of fluid apertures; and astructure, within the tip electrode, configured such that fluid passeddistally through a lumen of the catheter flows in a longitudinaldirection through a space between the structure and an inner surface ofthe tip electrode, prior to exiting through the fluid apertures.
 2. Theapparatus according to claim 1, wherein the structure is configured suchthat fluid flows through the space in a distal direction.
 3. Theapparatus according to claim 1, wherein the structure is configured suchthat the fluid flows through the space in a proximal direction.
 4. Theapparatus according to claim 1, wherein the structure comprises aconduit.
 5. The apparatus according to claim 4, wherein the conduit isconfigured such that the fluid exits a distal opening of the conduit,and is then deflected into the space by a distal face of the tipelectrode.
 6. The apparatus according to claim 5, wherein a majority ofthe fluid apertures are in a circumferential face of the tip electrode.7. The apparatus according to claim 5, wherein the distal opening of theconduit is positioned within 0.3 mm of the distal face of the tipelectrode.
 8. The apparatus according to claim 1, wherein the structureis shaped to define one or more circumferential openings, such that thefluid flows into the space through the circumferential openings.
 9. Theapparatus according to claim 1, wherein the space is less than 0.3 mm ina radial direction.
 10. The apparatus according to claim 1, wherein atleast part of the space is less than 0.1 mm in a radial direction.
 11. Amethod, comprising: using a tip electrode at a distal end of a catheter,passing an ablating signal into tissue; and while passing the ablatingsignal into the tissue, causing fluid to flow in a longitudinaldirection through a space between a structure and an inner surface ofthe tip electrode, and to subsequently exit the tip electrode throughfluid apertures in the tip electrode.
 12. The method according to claim11, wherein causing the fluid to flow in the longitudinal directioncomprises causing the fluid to flow in a distal direction.
 13. Themethod according to claim 11, wherein causing the fluid to flow in thelongitudinal direction comprises causing the fluid to flow in a proximaldirection.
 14. The method according to claim 11, wherein the structureincludes a conduit, and wherein the method further comprises causing thefluid to flow through the conduit prior to flowing through the space.15. The method according to claim 14, further comprising causing thefluid to exit a distal opening of the conduit, and to be deflected intothe space by a distal face of the tip electrode.
 16. The methodaccording to claim 15, wherein the distal opening of the conduit ispositioned within 0.3 mm of the distal face of the tip electrode. 17.The method according to claim 11, further comprising causing the fluidto flow into the space through one or more circumferential openings inthe structure.
 18. The method according to claim 11, wherein a majorityof the fluid apertures are in a circumferential face of the tipelectrode.
 19. The method according to claim 11, wherein the space isless than 0.3 mm in a radial direction.
 20. The method according toclaim 11, wherein at least part of the space is less than 0.1 mm in aradial direction.